In DE 197 47 838 A1, a method is described for the dry removal of coatings, graffiti or other surface contaminants from planar or curved surfaces. An abrasive or similar blast medium is supplied to a carrier air stream passed through a flexible piping system, is accelerated and is thrown against the surface to be treated.
The blast medium is then returned by a subatmospheric pressure of 50 to 300 mbar in the carrier air stream, is cleaned in a cleaning unit and is metered anew into the carrier air stream so that a circulation is obtained. The blast medium/air mixture is, before impinging on the surface to be treated, subjected to a linear acceleration to a jet speed of 20 to 80 m/s whereby the acceleration is obtained by a reduction in the diameter from the feed line stretch to the accelerating stretch.
The jet velocity which is achieved by means of this diameter reduction is indeed sufficient for the removal of graffiti or other surface contaminants by an abrasive effect. For the removal or leveling of harder surfaces, like for example solder and weld seams, however, the jet velocity which is produced is too low so that the known method is uneconomical. This applies also to the descaling of metallic surfaces or the removal of contaminated concrete layers.
The energy input achieved in accordance with DE 197 47 838 A1 is, on the other hand, much too high when point-like inclusions in a paint layer are to be removed. Multilayer paint layers are, as is known, up to 150 μm thick and are comprised, from the outside inwardly of a clear lacquer and a base lacquer layer, a filler and a primer layer. Especially in the case of metallic lacquering of automobile body parts, defect locations can arise in the application of the paint which above all have their origins in point-like or flat inclusions in the clear lacquer or base lacquer layer. These defects can give rise to the need for expensive and costly processing because the diameter reduction enables only a limited control of the jet speed so that on the one hand with an impingement energy which is selected to be too high, the entire lacquer layer is damaged or affected while on the other hand with too small an impingement energy the treatment is uneconomical.